A ground fault circuit interrupter (GFCI) is designed to prevent shock or electrocution by detecting an unintended conductive path between an ungrounded current carrying conductor and earth ground. Arc fault circuit interrupters (AFCI), on the other hand, are designed to prevent fires by detecting an unintended electrical arc. Multifunction circuit breakers combine the functionality of both GFCI circuit breakers and AFCI circuit breakers, as well as other functionality, into a single circuit breaker device. These various circuit breaker devices share a common purpose of tripping or disconnecting power to a load when a ground fault or an arc fault is detected. To ensure proper functionality, these circuit breaker devices are provided with an internal self-test input that users may initiate to check whether the devices are operating as intended. Tripping these circuit breaker devices during the self-test signifies the devices are operating properly.
Existing multifunction circuit breaker devices use a separate test input to initiate each self-test sequence, one for the arc fault self-test sequence and another for the ground fault self-test sequence. The test inputs may be implemented using either a plurality of test buttons, one button for each test, or a single test button having multiple button positions, one button position for a first test and another button position for a second test. This approach requires additional hardware components and board space that render the circuit breaker devices unnecessarily complex and costly. Each additional test button would need extra components to mount the test button to the device's housing and couple the test button to the device's microcontroller, which increases manufacturing costs and complicates design considerations. Likewise, a single test button with multiple button positions also requires extra hardware components and complicates design considerations.
Single-button solutions are available in some circuit breaker devices that use one test input to initiate both arc fault and ground fault self-test sequences. An example of such a device is the AFCI circuit breaker device described in commonly-assigned U.S. Pat. No. 8,035,936, incorporated herein by reference. But a single-button solution for both the arc fault and ground fault self-test sequences is problematic for existing multifunction devices, as successful completion of either self-test sequence would trip the circuit breaker, possibly giving users the incorrect impression that all self-test sequences have passed in the device. It would be more useful instead to be able to delay or prevent the tripping associated with a successful ground fault self-test sequence until all self-test sequences have actually passed. Alas, industry standards such as UL 943 make it difficult to do this.
Presently, industry standards such as UL 943 require circuit breaker devices to include a test circuit or “supervisory circuit” that may be used to test the ground fault detection capability of the devices. The supervisory circuit is designed to introduce a predefined amount of current into the circuit breaker device that simulates a ground fault event. The UL 943 specified maximum ground fault trip current is 6 mA RMS, so the predefined amount of current introduced by the supervisory circuit of most circuit breaker devices is set to at least 6 mA RMS to ensure the devices trip during ground fault self-testing. This makes the simulated ground fault current virtually indistinguishable from an actual ground fault current to the circuit breaker devices, so the devices trip upon successful completion of the ground fault self-test sequence regardless of whether the arc fault self-test sequence (or any other self-test sequence) has passed. Consequently, single-button solutions have not previously been feasible in multifunction circuit breakers.
A need therefore exists for an improved multifunction circuit breaker device that is capable of performing multiple user-initiated self-test sequences from a single test input, and that is capable of distinguishing between a simulated ground fault and an actual ground fault. The disclosed embodiments satisfy one or more of these needs and solve other problems as well.